Apparatus for forming low-temperature oxide films and method of forming low-temperature oxide films

ABSTRACT

The present invention aims at providing an apparatus for and a method of forming low-temperature oxide films, which are capable of forming an oxide film at a low temperature and preventing the diffusion of impurities from the outside. The apparatus for forming an oxide film at a low temperature is characterized in that it has an oxidation furnace provided with a gas supply port and a gas discharge port, a heater for heating the oxidation furnace to a predetermined temperature, and a gas supply system disposed upstream of the oxidation furnace and provided with a means for adding an arbitrary quantity of water or a means for generating an arbitrary quantity of water.

TECHNICAL FIELD

The present invention relates to an apparatus for forminglow-temperature oxide films and a method of forming low-temperatureoxide films which are capable of forming an oxide film on a sample atlow temperatures, and in particular, relates to an apparatus for forminglow-temperature oxide films and a method of forming low-temperatureoxide films which are capable of forming highly pure oxide films at lowtemperatures when forming oxide films on substrates in semiconductormanufacturing processes or the like.

BACKGROUND ART

Silicon oxide technology is one of the fundamental technologies insilicon device manufacturing processes; a large amount of research hasbeen conducted in this field. However, the fact that research is beingwidely conducted even at present into topics ranging from surfaceproblems to application indicates that silicon oxide technology has notyet been perfected.

In concert with miniaturization, the characteristics of devices areliable to be influenced by crystal defects in the substrate, andfurthermore, as the diameter increases, twisting or warping in thesilicon wafers leads to a worsening of the precision of reticlealignment, and an increase in process performance becomes difficult. Itis thought that these problems will be exaggerated by the hightemperature heat treatment of silicon substrates. Furthermore, in hightemperature processes, the diffusion of impurities from the outside, andthe like, is likely to occur, and ideal surfaces and thin film formationbecome difficult.

A decrease in temperature of the semiconductor processes is an effectivemethod of solving such problems, and a reduction in the temperature ofsilicon oxide film formation is an important objective.

Presently, the formation of silicon oxide films is conducted by means ofdry oxidation at high temperatures of 800° C. or more, and by means ofwet oxidation, in which hydrogen is caused to combust in an oxygenatmosphere at a temperature of 700° C. or more, water vapor isgenerated, and oxidation occurs. It is known that in comparison with dryoxidation, the growth rate of the oxide film is higher in wet oxidation.Accordingly, wet oxidation was more effective when forming oxide filmsat low temperatures using conventional technology. However, in wetoxidation, since the combustion of hydrogen is carried out, thetemperature must necessarily be that of the combustion of hydrogen, 700°C., or more.

Furthermore, oxidation processing is conducted under high pressure inorder to form an oxide film having a greater film thickness at lowtemperatures. However, because a double walled structure comprising aquartz oxidation furnace and a stainless steel furnace was employed insuch cases, impurities passed from the inner surface of the stainlesssteel through the quartz and were diffused, so that it was difficult toform highly pure oxide films.

Accordingly, in the conventional oxidation methods, large problems werecaused by high temperature processing at temperatures of 700° C. or moreand the fact that as a result, impurities passed through the quartz tubefrom the outside, and were diffused, and thus a highly pure atmospherecould not be formed.

The present invention has as an object thereof to provide an apparatusfor forming low-temperature oxide films and a formation method which arecapable of forming oxide films at low temperatures, and furthermoreprevent the diffusion of impurities from the outside.

DISCLOSURE OF THE INVENTION

The apparatus for forming low-temperature oxide films in accordance withthe present invention is an apparatus for forming oxide films at lowtemperatures, characterized in being provided with: an oxidation furnacepossessing a gas supply port and a gas exhaust port; a heater forheating said oxidation furnace to an arbitrary temperature; and a gassupply system disposed upstream of said oxidation furnace and providedwith a mechanism for adding an arbitrary quantity of water or amechanism for generating an arbitrary quantity of water.

The method of forming low-temperature oxide films in accordance with thepresent invention is characterized in comprising: a gas supply processfor supplying a gas containing water and oxygen to the interior of theoxidation furnace of an apparatus for forming low-temperature oxidefilms comprising an apparatus for forming oxide films at lowtemperatures provided with an oxidation furnace having a gas supply portand a gas exhaust port, a heater for heating the oxidation furnace to anarbitrary temperature, and a gas supply system disposed upstream of theoxidation furnace and provided with a mechanism for providing anarbitrary amount of water or a mechanism for generating an arbitraryquantity of water; and a thermal oxidation process for heating andoxidizing a sample within said oxidation furnace.

Function

The apparatus for forming low-temperature oxide films in accordance withthe present invention is capable of conducting the thermal oxidationprocess in a highly pure manner and at high pressures of 1 kg/cm² ormore, as a result of the fact that the oxidation furnace and the gassupply system comprise metallic materials and that a mechanism isprovided for generating water vapor at low temperatures. Accordingly, amixed gas of water vapor and oxygen is supplied to the oxidation furnaceat low temperatures of 600° C. or less, and it is possible to form ahighly pure oxide film.

Embodiment Examples

Hereinbelow, embodiment examples will be explained using the Figures.

FIG. 1 is a conceptual diagram of an apparatus showing an embodimentexample of the present invention; it depicts an apparatus for forming anoxide film on a semiconductor at low temperatures.

The apparatus 1100 for forming low-temperature oxide films comprises anoxidation furnace 1101, an oxidation furnace heater 1102, a pipingsystem 1103 comprising piping 1103a and mass flow controllers (MFC)1103b-1103e, and piping heater 1104. Gas introduction port 1105 and gasexhaust port 1106 are attached to oxidation heater 1101, and pressureregulator 1107 is attached to the piping of gas exhaust port 1106 sothat it is possible to conduct oxidation processing under high pressure.

First, the method of generating water vapor will be explained. Nitrogen,argon, oxygen, and hydrogen gases are supplied to piping system 1103,and the flow rates thereof are controlled by MFC 1103b-1103erespectively. The water vapor is generated by heating the piping 1103ahaving an atmosphere containing an arbitrary concentration of oxygen gasto a temperature within a range of 200° C.-600° C. using heater 1104,and adding an arbitrary concentration of hydrogen to piping 1103a. Thehydrogen is dissociated by the catalytic action of the stainless steelpipe, and may be completely dissociated if it is present at lowconcentrations, so that for example, it is possible to generate 1% ofwater vapor with respect to a hydrogen concentration of 1%.

Next, an example of a method for oxide film formation at lowtemperatures will be explained. The water vapor which was generated inaccordance with the above outline in the case of humidificationoxidation under normal pressures is supplied, in the form of, forexample, a mixed gas with oxygen, from gas introduction port 1105 tooxidation furnace 1101. The temperature within oxidation furnace 1101 iscontrolled so as to be 600° C. or less by means of heater 1102, andhumidification oxidation at low temperatures takes place. Here, theoxidation temperature and the mixing ratio of the water vapor and oxygenare variable, and it is also possible to add argon or nitrogen.

Furthermore, when processing under high temperatures, the pressure isset to an arbitrary level using the pressure regulator 1107 which isattached to gas exhaust port 1106, and the pressure within oxidation1101 is placed at a setting value. Here, the mixing ratio of the gasesand the oxidation temperature are variable at 600° C. or less.

BRIEF DESCRIPTION OF THE DIAGRAMS

FIG. 1 is a conceptual diagram showing an embodiment example of theapparatus of the present invention.

FIG. 2 is a graph showing the amount of water vapor generated whenamounts of hydrogen in a range of 100 ppm/1% were added to a mixed gasof 99% argon and 1% oxygen in Embodiment 1.

FIG. 3 is a graph showing the oxide film thickness.

FIG. 4 is a table showing the state of the metal contamination.

FIG. 5 is a graph showing the insulation pressure resistance ofinsulating films of MOS formed by means of an embodiment of the methodof the present invention.

FIG. 6 is a conceptual diagram of a standard water generating apparatusin accordance with Example 1.

FIG. 7 shows the results of a measurement of water concentration in thegas flowing from a standard water generating apparatus in accordancewith Example 1.

FIG. 8 shows the results of a measurement of oxygen concentration in agas flowing from a standard water generating apparatus in accordancewith Example 1.

FIG. 9 is a conceptual diagram of a standard water generating apparatusin accordance with Example 2.

FIG. 10 is a conceptual diagram of a standard water generating apparatusin accordance with Example 3.

FIG. 11 is a conceptual diagram of a standard water generating apparatusin accordance with Example 4.

FIG. 12 is a conceptual diagram of a standard water generating apparatusin accordance with Example 5.

FIG. 13 shows the results of a measurement of water concentration in agas flowing from a standard water generating apparatus in accordancewith Example 5.

FIG. 14 shows the results of a measurement of hydrogen concentration ina gas flowing from a standard water generating apparatus in accordancewith Example 5.

FIG. 15 is a conceptual diagram of a standard water generating apparatusin accordance with Example 6.

FIG. 16 is a conceptual diagram of a standard water generating apparatusin accordance with Example 7.

FIG. 17 is a conceptual diagram of a standard water generating apparatusin accordance with Example 8.

(Description of the References)

    ______________________________________                                        1100        apparatus for forming low-temperature oxide                                   films,                                                            1101        oxidation furnace,                                                1102        oxidation furnace heater,                                         1103        piping system,                                                    1103a       piping,                                                           1103b-1103e mass flow controllers (MFC),                                      1104        piping heater                                                     1105        gas introduction port,                                            1106        gas exhaust port,                                                 1107        pressure regulator.                                               101         mass flow controller (MFC),                                       102         mass flow controller,                                             103         mass flow controller,                                             104         mixing pipe,                                                      105         reactor,                                                          106         optical dew-point meter (water                                                concentration meter),                                             107         galvanic battery type oxygen analyzer,                            200         reactor,                                                          400         reactor,                                                          401         mass flow controller,                                             500         reactor,                                                          501         mass flow controller,                                             600         reactor.                                                          ______________________________________                                    

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, embodiments of the present invention will be given.

Embodiment 1

In FIG. 2, the amount of water vapor generated when an amount ofhydrogen within a range of 100 ppm-1% was added to a mixed gas of 99%argon and 1% oxygen is shown. Here, the temperature of the piping waswithin a range of 200°-400° C.

This indicates that hydrogen can be dissociated by means of thecatalytic effect of stainless steel even at temperatures below 700° C.,the combustion temperature of hydrogen, and can be reacted with oxygento form water vapor. Furthermore, the Figure shows that dissociation iscomplete at a temperature of 450° C.

Embodiment 2

FIG. 3 shows the oxide film thickness when oxidation was conducted at atemperature of 600° C. and for a period of one hour, in a gas comprising99% oxygen and 1% water vapor, where the oxidation pressure was a normalpressure, and an elevated pressure of 3 kg/cm². For the purposes ofcomparison, a case was also considered in which an oxide film was formedin a conventional quartz oxidation furnace at identical oxidationtemperatures and periods, in a gas composed of solely oxygen and atnormal pressures.

This indicates that the speed of oxidation is increased by adding watervapor to oxygen, and that the speed of oxidation is further increased byhigher pressures.

Embodiment 3

The state of metallic contamination of an oxide film formed in aconventional quartz furnace and oxide film in accordance with the methodof the present invention were compared. The oxidation conditions wereidentical to those described in Embodiment 2, respectively. The resultsare shown in FIG. 4.

In the case in which the method of oxidation employing a conventionalfurnace was employed, Cu contamination was particularly notable;however, the case in which the oxidation method of the present inventionwas employed exhibited reduced contamination, apart from Cr. Comparingthe two cases, it can be seen that metallic contamination was completelysuppressed by the use of the oxidation method in accordance with thepresent invention.

Embodiment 4

The insulation pressure resistance characteristics of MOS diodesemploying an oxide film formed in a conventional quartz furnace, and anoxide film formed at low oxide film temperatures by means of the presentinvention, are shown in FIG. 5.

As described above, by means of the use of the apparatus for forminglow-temperature oxide films in accordance with the present Embodiment,it is possible to form an oxide film at low temperatures, and it ispossible to form a highly pure oxide film.

Hereinbelow, examples of a water generating method and apparatus will bediscussed. These may be applied to Embodiments 1-4.

EXAMPLE 1

The present Example refers to the case in which an arbitrary waterconcentration is generated using a mixed gas of oxygen, hydrogen, andargon; a conceptual diagram of the apparatus is shown in FIG. 6. Asshown in FIG. 6, the flow rate of the oxygen gas is controlled by massflow controller (MFC) 101, the flow rate of the hydrogen gas iscontrolled by mass flow controller 102, and the flow rate of the argongas is controlled by mass flow controller 103; the three types of gasespass through mixing pipe 104 where they are mixed, and are introduced toreactor 105. In reactor 105, the hydrogen and oxygen are reacted, and amixed gas of hydrogen and argon containing an arbitrary amount of wateris generated. An SUS 316L stainless steel pipe (the inner surfaces ofwhich were subjected to electrolytic polishing) having a diameter of1/4" and a length of 2 m was used as reactor 105, and a reduction inreaction temperature was realized using the catalytic action of theinner surface of the stainless steel pipe.

The flow rates of the hydrogen gas and the argon gas were set at,respectively, 50 cc/min and 450 cc/min using mass flow controllers 102and 103, and varying only the flow rate of the oxygen gas within a rangeof 0.1-10 cc/min using mass flow controller 101, three types of mixedgases were introduced into the reactor, and the water concentration andoxygen concentration contained in the mixed gas of hydrogen and argonflowing from the reactor were measured using an optical dew-point meter(water concentration meter) 106 and a galvanic battery type oxygenanalyzer 107. The hydrogen, oxygen, and inert gasses employed were allsuper pure gasses having an impurity concentration of 1 ppb or less. Thetemperature of reactor 105 was maintained at 300° C. over the entirelength thereof.

The results of this measurement are shown in FIGS. 7 and 8. Thehorizontal axis indicates the oxygen concentration in the mixed gas ofhydrogen, oxygen, and argon, and the vertical axis indicates thehydrogen concentration in the gas flowing from reactor 105. In FIG. 8,the horizontal axis indicates the oxygen concentration in the gassupplied to reactor 105, and the vertical axis indicates the oxygenconcentration flowing from reactor 105. From the results of FIG. 7, itcan be seen that water was detected in the gas flowing from the reactorat a concentration which was twice the oxygen concentration which wassupplied to reactor 105. The water generation concentration was within arange of 100 ppb-2%.

FIG. 8 shows that no matter what the concentration of oxygen supplied toreactor 105, absolutely no oxygen was detected in the gas flowing fromreactor 105. That is to say, it was found that a complete reaction ofthe hydrogen and oxygen occurred in the reactor, and the water which wasgenerated depended on the oxygen concentration supplied to reactor 105.

From these facts, it was determined that in the present Example, it waspossible to generate a mixed gas containing an arbitrary concentrationof super pure water by means of adjusting the oxygen concentrationsupplied to reactor 105 using mass flow controller 101.

In the present Example, the temperature of reactor 105 was set at 300°C.; however, even an a temperature of 100° C., identical results wereobtained, and it was found that when stainless steel materials were usedin reactor 105, any temperature within a range of 100° C.-500° C. wasappropriate for use for the temperature of reactor 105.

In the above Example, 100% facility piping super pure gasses were usedas the hydrogen, oxygen, and argon (inert gas) gasses; however, it isalso possible to use gas tanks having a 100% concentration of thesegases, or mixed gas tanks.

Furthermore, the temperature of reactor 105 was set to 300° C.; however,this temperature is closely related to the flow rate of supplied gassesand the volume of the reaction pipe (reaction time), so that there arecases in which the temperature may be less than 300° C.

Furthermore, SUS 316L material was used as the material for the reactorin the present Example; however, any metal may be used insofar as it hasa catalytic action which permits a lowering of the temperature ofreaction between hydrogen and oxygen. For example, Hastelloy, nickel,platinum, or the like may be used. Furthermore, the entirety of thereaction pipe need not employ metal having a catalytic action; it isacceptable if such metal is used in only a portion of the reaction pipe,for example on those surfaces which are in contact with gas.

EXAMPLE 2

In the present Example, the interior of the reactor is filled withcatalytic metal in order to reduce the reaction temperature of hydrogenand oxygen gas; a reactor 200, comprising the reactor of Example 1provided with platinum fiber catalytic material, is employed. Aconceptual diagram of the apparatus is shown in FIG. 9. Other points areidentical to those in Example 1. It was confirmed that a completereaction of the hydrogen and oxygen took place even when the temperatureof the reactor 200 was 200° C.

EXAMPLE 3

In the present Example, a dilution apparatus is provided upstream fromthe mass flow controller for hydrogen gas supply, thus making itpossible to supply hydrogen gas at low concentrations, and to reduce thewater concentration which is generated.

When this concentration is reduced, the release of water from the innerwalls of the piping or the reactor cannot be ignored. In particular,when the temperature of the piping or reactor changes, the amount ofwater released from the inner walls changes, so that it is impossible toconduct water generation at stable concentrations. In the presentExample, the entirety of the water generating apparatus is disposedwithin a constant temperature bath, and the amount of water releasedfrom the inner walls of the piping or the reactor is maintained at aconstant level. A conceptual diagram of the apparatus is shown in FIG.10.

Other points are identical to those of Example 1. As a result ofconducting an evaluation identical to that of Example 1, it wasconfirmed that because it was possible to reduce the concentration ofhydrogen gas which was supplied, water generation became possible withina concentration range of from 10 ppt to 2%, in comparison to theconcentration range of water generation of Example 1, which was 100ppb-2%.

Furthermore, it was confirmed that by maintaining the water generatingapparatus at an arbitrary constant temperature, both water generation atconcentrations of 2% or more and water generation at stable lowconcentrations was possible.

EXAMPLE 4

In the present Example, gas containing an arbitrary amount of generatedwater can be supplied at a arbitrary flow rate; a conceptual diagramthereof is shown in FIG. 11. As in Example 1, a mass flow controller 401is provided downstream from reactor 400 together with a blowoff pipe 402for blowing off a portion of the gasses flowing from the reactor inorder to maintain the pressure between the mass flow controller 401 andthe reactor 400 at a constant level.

Other points are identical to those of Example 1. By using the apparatusshown in FIG. 11, it was possible to control the flow rate of the gascontaining water, and to supply gas containing an arbitrary waterconcentration at an arbitrary flow rate. For example, in the case inwhich the full scale of mass flow controller 401 was 100 cc/min, it wasconfirmed that flow rate control was possible within a range of from 0.1to 100 cc/min. When the full scale of mass flow controller 401 was 2L/min, it was confirmed that flow rate control was possible within arange of 2 cc/min-2 L/min.

EXAMPLE 5

In the present Example, by adjusting the hydrogen concentration, thewater concentration which is generated is adjusted. In Examples 1through 4, an excessive hydrogen concentration was supplied, and thewater concentration was determined by the oxygen concentrations;however, here, in a state in which the oxygen concentration wasexcessive (in the present embodiment, an oxygen concentration of 10%),the water concentration flowing from reactor 500 was controlled by meansof the hydrogen concentration which was supplied. In contrast, in thepresent invention, the reactor temperature was set to 400° C. Aconceptual diagram of the apparatus is shown in FIG. 12. The results ofthe evaluation are shown in FIGS. 13 and 14. It can be seen from theresults of FIG. 13 that water was detected in the gas flowing fromreactor 500 at a concentration which was equal to the hydrogenconcentration supplied to reactor 500. The concentration of watergenerated was within a range of 100 ppb-1%. From the results of FIG. 14,it can be seen that absolutely no hydrogen gas was detected in the gasflowing from reactor 500 no matter what the concentration of hydrogensupplied to reactor 500. That is to say, a complete reaction of thehydrogen and oxygen occurred in reactor 500, and water was generated inproportion to the hydrogen concentration supplied to reactor 500.

It can be seen from these facts that the apparatus of the presentExample is applicable to an apparatus for generating a mixed gascontaining an arbitrary amount of super pure water by controlling thehydrogen concentration supplied to reactor 500 in the apparatus of thepresent invention using mass flow controller 501.

Furthermore, it was confirmed that the present Example was applicable toan apparatus for generating a mixed gas containing an arbitrary amountof super pure water even when the ratio of hydrogen flow rate to oxygengas flow rate was 2 to 1.

EXAMPLE 6

In the present Embodiment, the hydrogen gas or oxygen gas remaining inthe gas containing water which is generated is removed; in the case inwhich, as in Examples 1-5, one or the other hydrogen gas or oxygen gasis in excess during the reaction, there are cases in which thisexcessive hydrogen or oxygen component remains in the gas containing thewater which is generated. Accordingly, a refining apparatus 601 which iscapable of selectively removing hydrogen or oxygen is installeddownstream from reactor 600, and the apparatus supplies gas containingan arbitrary water concentration and which does not contain hydrogen oroxygen; this apparatus is shown in FIG. 15. The generation of a gascontaining only water, and neither hydrogen or oxygen, was confirmed.

EXAMPLE 7

The present Example relates to a standard water generating apparatusprovided with a gas stopping function; FIG. 16 shows a conceptualdiagram of this standard water generating apparatus which is providedwith metal stop valves, in consideration of cases in which it isdesirable to stop the gases, with respect to Examples 1-6. Thegeneration of a gas containing an arbitrary amount of water wasconfirmed.

EXAMPLE 8

In the present Example, in order to accelerate the startup of thestandard water generating apparatus, the interior of the standard watergenerating apparatus is purged with an inert gas, or at least a portionof the standard water generating apparatus is subjected to baking; thestructure of the apparatus is identical to that shown in FIG. 11, and isdepicted again in FIG. 17. The stable generation of a gas containing 1ppm of water was confirmed within 30 minutes from the startup of thestandard water generating apparatus.

Furthermore, at this time, in the case in which plastic materials arecompletely eliminated from the portions in contact with gas, and onlymetallic materials are employed, and furthermore, passivation processingis conducted with respect to the metallic surfaces, only an extremelysmall amount of gases are released from the surfaces (water,hydrocarbons, and the like), and it becomes possible to generate morehighly pure water with a higher degree of precision and within a broaderconcentration range (ppb-%).

Such passivation processing may be conducted by, for example, thethermal treatment, in an oxidizing or weakly oxidizing atmosphere havingan impurity concentration of a few ppb or less, of SUS 316L which hasbeen subjected to electrolytic polishing or electrolytic compositepolishing (as in, for example, Japanese Patent Application No. Sho63-5389 (Japanese Patent Application, First Publication No. Hei2-85358), and PCT/JP92/699 (WO92-21786), and Japanese Patent ApplicationNo. Hei 4-164377).

It should be particularly noted that such passivated films, in additionto the fact that an extremely small amount of water is released from thesurfaces thereof, have surfaces which themselves act to create hydrogenand oxygen radicals. Accordingly, the use of a reactor pipe having suchpassivated films on the inner surfaces thereof is extremely effective ingenerating water with high precision. In this way, the fact that it isnot the base material itself, but rather the oxides of the base elementsformed on the surface thereof, which possess the catalytic actioncapable of creating hydrogen and oxygen radicals, is not easilyunderstood, and is surprising; in the present invention, skillfuladvantage is taken of characteristics such as the small amount of waterreleased from the surfaces, and this catalytic action.

Industrial Applicability

In accordance with the present invention, semiconductors or metals canbe oxidized in a highly pure atmosphere and at low temperatures. Theeffects of crystal defects in the silicon substrate or warping ortwisting of the silicon wafer can be suppressed, and more productiveprocesses become possible. Furthermore, it is to be expected that byreducing the temperature of the oxidizing process, a simplification ofthe semiconductor manufacturing line will occur.

I claim:
 1. A method of forming silicon oxide films, comprising thesteps of supplying a gas containing water and oxygen to the interior ofan oxidation furnace of an apparatus for forming low-temperature oxidefilms; said oxidation furnace having a gas supply port and a gas exhaustport, and a heater for heating said oxidation furnace to an arbitrarytemperature, said apparatus further comprising a gas supply systemdisposed upstream of said oxidation furnace and provided with amechanism for providing an arbitrary amount of water or a mechanism forgenerating an arbitrary quantity of water, said oxidation furnace, saidgas supply system and junction portions thereof being constructed ofmetallic materials; andheating and oxidizing a sample within saidoxidation furnace at low temperatures of 600° C. or less and underpressures of 1 kg/cm² or more.
 2. A method of forming silicon oxidefilms in accordance with claim 1, wherein said gas is supplied at waterconcentrations within a range of 0.1-5 vol. %, and oxygen concentrationsof 1 vol. % or more.
 3. An apparatus for forming silicon oxide filmscomprising an oxidation furnace having a gas supply port and a gasexhaust port; a heater for heating said oxidation furnace to anarbitrary temperature; and a gas supply system disposed upstream of saidfurnace and provided with a mechanism for adding for generating anarbitrary quantity of water;said oxidation furnace, said gas supplysystem, and junction portions thereof comprise metallic materials anddiffusion of impurities from outside the system is completelyeliminated.
 4. An apparatus for forming silicon oxide films according toclaim 3, wherein inner surfaces of said oxidation furnace and said gassupply system are covered with a thermal oxide passivated film.
 5. Anapparatus for forming silicon oxide films according to claim 3, whereinparts in said gas supply system are made of stainless steel.
 6. Anapparatus for forming silicon oxide films comprising an oxidationfurnace having a gas supply port and a gas exhaust port; a heater forheating said oxidation furnace to an arbitrary temperature; and a gassupply system disposed upstream of said oxidation furnace and providedwith a mechanism for generating an arbitrary quantity of water;whereinsaid oxidation furnace, said gas supply system, and junction portionsthereof comprise metallic materials; and wherein said gas supply systemcomprises a reactor capable of generating an arbitary amount of water bymeans of a catalytic reaction between oxygen and hydrogen at atemperature of 500° C. or less, and a heater for heating said reactor.7. An apparatus for forming silicon oxide films according to claim 6,wherein parts in said gas supply system are made of stainless steel.